Added support for changelog

app/com/ysoft/odc/SetDiff.scala

@@ -5,4 +5,10 @@ class SetDiff[T](val oldSet: Set[T], val newSet: Set[T]) {
   lazy val removed = oldSet -- newSet
   lazy val isEmpty = newSet == oldSet
   def nonEmpty = !isEmpty
+
+  def map[U](f: T => U): SetDiff[U] = new SetDiff[U](
+    oldSet = oldSet.map(f),
+    newSet = newSet.map(f)
+  )
+
 }